Wireless Transfer of Power and Data Via a Single Resonant Inductive Link

A novel circuit design for wireless power and signal transfer using a single resonant inductive link is presented. On the transmitter side, a self-oscillating relay feedback circuit automatically generates a carrier signal near the resonance and drives the transmitter coil. A tunable phase shifter made of two cascaded first-order allpass filters is inserted in the relay feedback loop to modulate the carrier amplitude in accordance with the input signal. On the receiver side, a bridge rectifier and a voltage regulator are used for AC-to-DC power conversion, and also a bandpass filter is added to perform amplitude demodulation for extracting the signal from the carrier. The proposed 1.1MHz inductive link has been successfully implemented on a 2.5W wireless speaker. It allows music being played on a speaker without any connection to a power cable and an audio line. The measurement shows that the total harmonic distortion plus noise for a 1kHz sinusoidal signal being transferred can be as low as 1%.